1. Field of the Invention
The present invention relates to a light emitting device and a method of driving the same, more particularly relates to a light emitting device for preventing cross-talk phenomenon and a method of driving the same.
2. Description of the Related Art
A light emitting device emits a light having a certain wavelength. Especially, an organic electroluminescent device as the light emitting device is self light emitting device.
FIG. 1 is a sectional view illustrating schematically pixel included in a common organic electroluminescent device. FIG. 2 is a view illustrating schematically a circuitry of a passive-matrix type organic electroluminescent device. FIG. 3 is a timing diagram illustrating a process of driving the organic electroluminescent device.
In FIG. 2, the organic electroluminescent device includes a plurality of pixels 10.
Each of the pixels 10 includes an anode electrode layer 2, an hole transporting layer 3, an emitting layer 4, an electron transporting layer 5 and a cathode electrode layer 6 formed in sequence on an substrate 1 as shown in FIG. 1.
The anode electrode layer 2, the emitting layer 4 and the cathode electrode layer 6 are made up of transparent conductive material, organic material, and metal, respectively.
When a certain positive voltage and a negative voltage are provided to the anode electrode layer 2 and the cathode electrode layer 6, respectively, the hole transporting layer 3 transports holes generated from the anode electrode layer 2 to the emitting layer 4. In addition, the electron transporting layer 5 transports electrons generated from the cathode electrode layers 6 to the emitting layer 4. Subsequently, the transported holes and the transported electrons are recombined in the emitting layer 4, and so a light having a certain wavelength is emitted from the emitting layer 4.
There are a passive-matrix type organic electroluminescent device and an active-matrix type organic electroluminescent device as the organic electroluminescent device.
Hereinafter, the passive-matrix type organic electroluminescent device of the organic electroluminescent device will be described in detail.
In FIG. 2 and FIG. 3, the organic electroluminescent device includes a plurality of pixels 10 formed in cross areas of data lines D1 to Dm and scan lines S1 to Sn.
Scan signals SP1 to SPn are provided to the scan lines S1 to Sn, and so the scan lines S1 to Sn are connected in sequence to a ground.
Data signals, i.e. data current Id synchronized with the scan signals SP1 to SPn are provided to the data lines D1 to Dm. As a result, pixels corresponding to a scan line connected to the ground emits a light having the brightness corresponding to the data current Id.
A cross-talk phenomenon is occurred in the organic electroluminescent device. This will be explained in detail with reference to the accompanying drawings.
FIG. 4 is a plan view illustrating a picture displayed on the organic electroluminescent device.
In FIG. 4, a black picture is displayed on the center of the organic electroluminescent device, and a white picture is displayed on the other area thereof.
Hereinafter, a white picture area approximate to the black picture is assumed as a first white area A, and a white picture area over/under the first white area A is assumed as a second white area B.
Though data current having the same magnitude is provided to the first white area A and the second white area B so that light having the same brightness is emitted from the first white area A and the second white area B, the brightness of a light emitted from the first white area A is different from that of a light emitted from the second white area B. This is referred to as “Cross-talk phenomenon”. The cross-talk phenomenon will be described in more detail with reference to the accompanying drawing.
FIG. 5 is a timing diagram illustrating a process of driving the organic electroluminescent device.
As shown in FIG. 5, since the first white area A displays the black picture, the amount of first precharge current provided to one data line in a second precharge time of a scan signal SP2 provided to a N+1 scan line is smaller than that of second precharge current provided to the data line in a first precharge time of a scan signal SP1 provided to a N scan line. In other words, the magnitude at a start point of a second luminescent time corresponding to the N+1 scan line is smaller than that at a start point of a first luminescent time corresponding to the N scan line.
Subsequently, data current having the same magnitude is provided to the data line during the first and second luminescent times so that the first white area A and the second white area B have the same brightness.
However, though the data current having the same magnitude is provided to the data line, a first pixel corresponding to the N+1 scan line and the data line has the brightness different from a second pixel corresponding to the N scan line and the data line because the amount of the first precharge current is different from that of the second precharge current. In other words, though the first white area A and the second white area B are preset to have the same brightness, the brightness of the first white area A is different from that of the second white area B. Accordingly, the display characteristics of the organic electroluminescent device might be deteriorated by the cross-talk phenomenon.